Obesity is a well-known risk factor for the development of many very common diseases such as atherosclerosis, hypertension, type 2 diabetes (non-insulin dependent diabetes mellitus (NIDDM)), dyslipidemia, coronary heart disease, and osteoarthritis and various malignancies. It also causes considerable problems through reduced motility and decreased quality of life. The incidence of obesity and thereby also these diseases is increasing throughout the entire industrialised world.
The term obesity implies an excess of adipose tissue. In this context obesity is best viewed as any degree of excess adiposity that imparts a health risk. The cut off between normal and obese individuals can only be approximated, but the health risk imparted by the obesity is probably a continuum with increasing adiposity. In the context of the present invention, individuals with a body mass index (BMI=body weight in kilograms divided by the square of the height in meters) above 25 are to be regarded as obese.
Even mild obesity increases the risk for premature death and conditions such as diabetes, dyslipidemia, hypertension, atherosclerosis, gallbladder disease and certain types of cancer. In the industrialised western world the prevalence of obesity has increased significantly in the past few decades. Because of the high prevalence of obesity and its health consequences, its prevention and treatment should be a high public health priority.
Except for exercise, diet and food restriction, which is not feasible for a vast number of patients, no convincing treatment for reducing body weight effectively and acceptably currently exist. Only a few pharmacological treatments are available to date, namely Sibutramine (Abbot; acting via serotonergic and noradrenaline mechanisms), Orlistat (Roche Pharm; reducing fat uptake from the gut,) and Acomplia (rimonabant; Sanofi-Aventis; selective CB1 endocannabinoid receptor antagonist; approved in EU for use as an adjunct to diet and exercise in June 2006). However, not only in view of the considerable problems directly related to obesity as described above, but also due to the important effect of obesity as a risk factor in serious (even fatal) and common diseases, it is important to find pharmaceutical compounds which are useful in prevention and/or treatment of obesity.
When energy intake exceeds expenditure, the excess calories are stored predominately in adipose tissue, and if this net positive balance is prolonged, obesity results, i.e. there are two components to weight balance, and an abnormality on either side (intake or expenditure) can lead to obesity. This process may be counteracted by increasing the energy expenditure (for instance via exercise) or decreasing the energy intake (for instance by dieting). Pharmacological treatment available up to date only consists of Sibutramine (acting via serotonergic mechanisms, Abbott) and Orlistat (reducing fat uptake from the gut, Roche Pharm) neither reducing body weight effectively nor acceptably. There is therefore a need for pharmaceutical compounds which may be useful in prevention and/or treatment of obesity, for instance by increasing the energy expenditure or decreasing the energy intake.
One way of increasing energy expenditure is by increasing the metabolic rate. Oxidative phosphorylation in mitochondria, the energy from glucose metabolism and free fatty acids oxidation is used to drive the phosphorylation of ADP to ATP. When NADH and FADH2 formed in the TCA cycle are oxidised back to NAD+ and FAD respectively, protons are pumped out of the mitochondrial matrix. The resulting pH gradient (matrix pH˜8 and outside pH˜7) and potential (˜−170 mV, inside negative) across the inner mitochondrial membrane constitute the electrochemical proton gradient. As the effect of a one-unit pH difference corresponds to a potential of 61.5 mV, the electrochemical proton gradient exerts a proton-motive force of roughly −230 mV, which is the driving force for the mitochondrial ATP synthesis.
When the ATP consumption thus increases, the cells respond by increasing the ATP synthesis and consequently the inward flux of protons through the ATP synthase, the enzyme responsible for ATP synthesis and thereby the metabolic rate is increased. Chemical uncouplers are compounds, which can transport protons across membranes, and when protons are transported across the inner mitochondrial membrane, the ATP synthase is bypassed. At the (alkaline) matrix side the proton is released and the deprotonated uncoupler returns to the inter-membrane space where it picks up another proton. The cycling of the uncoupler (or ATP synthesis) and the resulting proton transport leads to an increased outward pumping of protons through an increased oxidation of NADH and FADH2 by the respiration chain. The NADH concentration in the matrix will consequently drop. Since NADH feed-back inhibits three steps in the TCA cycle (NADH is the main regulator of the TCA cycle), the flux through the TCA cycle will increase. Hence, the metabolic rate will increase.
Compounds, such as chemical uncouplers, which act by increasing the metabolic rate may thus be useful for treating obesity, but also for treating other conditions such as atherosclerosis, hypertension, diabetes, especially type 2 diabetes (NIDDM (non-insulin dependent diabetes mellitus)), dyslipidemia, coronary heart disease, gallbladder disease, osteoarthritis and various types of cancer such as endometrial, breast, prostate and colon cancers and the risk for premature death as well as other conditions, such as diseases and disorders, which conditions are improved by a reduced mitochondrial potential.
Furthermore, chemical uncouplers may reduce reactive oxygen species (ROS) that are assumed (De Grey et al, Eur J. Biochem 269, 1995 ff (2002)) to be involved in the aging process, in damage of heart tissue as well as neuronal tissue. It is therefore also possible that conditions affected by ROS may be reversed or halted by intervention by chemical uncouplers. Examples of such conditions include diabetic microvascular diseases in the retina, renal glomerulus and peripheral nerve cells.
Moreover, treatment with chemical uncouplers in combination with antibiotics or anticancer drugs may be beneficial in conditions, diseases of disorders where resistance to treatment with the latter types of drugs has developed. In the case of cancer treatments, a variety of chemotherapies are available to oncologists, and these are often capable of reducing the rate of tumor progression. However, development of intrinsic or acquired tumor-mediated drug resistance is a major clinical obstacle that can result in a lack of tumor responsiveness in patients undergoing treatment. The over-expression of efflux proteins, such as p-glycoprotein, is well recognized as contributing to the drug resistance process due to the ability of such proteins to pump cytotoxic therapeutic substances out of the cell.
Bacterial membrane efflux pump proteins form a large, heterogeneous family of energy-dependent membrane proteins capable of transporting either a single antibiotic, such as tetracycline, or a wide variety of chemically and structurally unrelated substances, out of bacterial cells, thereby enabling bacteria to adapt themselves to a hostile environment. In this connection, numerous compounds capable of inhibiting efflux pumps have been described. Some such compounds affect the electrochemical gradient across the membrane which serves as a source of energy for some efflux pumps, and examples of such compounds include the proton uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP).
The best known chemical uncoupler is 2,4-dinitrophenol (DNP), which has been shown to increase energy expenditure in humans as well as animals. The side effects at higher doses include increased perspiration, vasodilatation, skin rashes, cataracts, neuritis and even death. Two fatalities amongst the first 100.000 persons treated with DNP, and the fact that the lowest dose which could be lethal was only twice the average dose giving a desired 50% increase in basal metabolic rate, giving a very narrow safety window, combined with other factors led to the removal of DNP from the market. Since then nobody has attempted to develop or market uncouplers for the treatment of obesity.
DNP is the best known chemical uncoupler; but many other compounds are known to induce uncoupling. DNP derivatives such as 4,6-dinitro-o-cresol (Victoria Yellow) and 2,4-dinitro-1-naphtol (Martius Yellow) as well as structurally unrelated compounds such as 2,6-di-t-butyl-4-(2′,2′-dicyanovinyl)phenol) (SF6847) (also known as 2-(3,5-di-tert-butyl-4-hydroxybenzylidene)-malononitrile), carbonylcyanide m-chlorophenylhydrazone (CCCP) and carbonylcyanide ptrifluoromethoxy-phenylhydrazone (FCCP) (Miyoshi H et al. Quantitative relationship between protenophoric and uncoupling activities of analogs of SF6847 (2,6-di-t-butyl-4-(2′,2′-dicyanovinyl)phenol), Biochimica et Biophysica Acta 891, 293-299 (1987)) are uncouplers.
Another class of chemical uncouplers is the salicylanilides, of which S-13 is the most potent compound discovered so far (Terada H et al. Structural Requirements of Salicylanilides for Uncoupling Activity in Mitochondria Quantitative Analysis of Structure—Uncoupling Relationships, Biochimica et Biophysica Acta 936, 504-512 (1988)).
WO00/06143 to Texas Pharmaceuticals Inc. relates to a method for inducing intracellular hyperthermia comprising a step of administering a mitochondrial uncoupling agent, such as 2,4-dinitrophenol.
U.S. Pat. No. 4,673,691 to Bachynsky relates to the use of 2,4-dinitrophenol for treating obesity.
Various salicylic anilide derivatives have been disclosed in the literature. As an example, U.S. Pat. No. 4,025,647 discloses compounds of the formula
wherein R1 may be hydrogen, X is secondary or tertiary alkyl, R2 alkanoyl, phenylsulfinyl, phenylsulfonyl, etc, and Y is hydrogen or methyl. The compounds have anthelmintic activity, especially against liver fluke.
EP 322823 discloses electrophotographic photoreceptors with the following formula
wherein A is a group of atoms necessary to condense the benzene ring with another ring.
WO 01/44172 discloses compounds of the formula
wherein all X's may be carbon, R1 may be hydroxyl, R2-R5 may be optionally substituted aryl heteroaryl, alkylaryl, alkyl, ester, amide, etc. The compounds are inhibitors of serine proteases, urokinase, Factor Xa, Factor VIIa and have utility as anticancer agents and as anti-coagulants. R7 is amidine or guadinyl for all compounds specifically disclosed in this application.
WO 01/96944 discloses compounds of the formula
wherein R represent 0-4 substituents selected from alkyl, aryl, aralkyl, etc. The compounds are useful as components in colour photothermographic films. None of the specifically disclosed compounds have a branched alkyl or phenyl as substituent in the left-most phenyl ring.
WO 01/82924 discloses compounds of the formula
wherein R1-3 represents hydrogen, alkyl, halo, alkoxy, etc. The compounds are phosphate transport inhibitors.